A common way to diagnose interconnect defects (e.g., shorts and opens) in circuit assemblies (e.g., printed circuit boards, Multi-Chip Modules, and Silicon-in-Package devices) is via Boundary-Scan testing. A standard for Boundary-Scan testing is defined in IEEE Standard 1149.1.
As the electronics industry has moved forward with the implementation of AC coupled and differential networks, limitations in the techniques specified by IEEE Std. 1149.1 have become apparent. Specifically, IEEE Std. 1149.1 was designed to address the testing of single-ended, DC coupled networks, with no specific consideration of differential networks and explicit exclusion of AC coupled networks (an AC coupled network features a series capacitor or transformer to block DC current flow along the signal path, thereby allowing only AC signals to pass). A standard that defined how to apply Boundary-Scan techniques to AC coupled networks was therefore needed. To this end, IEEE Std. 1149.6 was developed. IEEE Std. 1149.6 specifies how to apply Boundary-Scan test principles to circuit assemblies comprising AC coupled and/or differential networks.
IEEE Std. 1149.6 is built upon the infrastructure of IEEE Std. 1149.1, but specifies the requirements of additional hardware to enable the creation and detection of signal transitions. These transitions, unlike constant voltage levels, can pass through AC coupling devices, and can thus be used to test the interconnection of components of an AC coupled network on a circuit assembly.